1. Field of the Invention
The present invention broadly pertains to a method of decontaminating soil by extracting the soil with a liquid solvent. More particularly, this invention consists of a method of decontaminating soil which has been contaminated with an organic hazardous waste, comprising contacting the soil with an aqueous ammonia solution to extract the organic hazardous waste from the soil.
2. Description of the Prior Art
Various methods have been employed to remove contaminants from soil. Wagner et al. (U.S. Pat. No. 4,392,892) discloses a method whereby soil, sand or residues that contain oil or petroleum hydrocarbons are impregnated with an aqueous solution containing microbially-produced glycolipids. The resulting oil phase or emulsion leaves the capillaries of the oil containing material, rises out of the aqueous phase, and is thereafter separated.
Giguere (U.S. Pat. No. 4,424,081) discloses a method for reconditioning soils contaminated with heavy crude, refined petroleum, and/or chemicall products derived from similar sources. The method involves mixing the soils with water, sodium hydroxide and steam to provide a blended slurry. The blended slurry is further agitated and heated in a sparger kiln to approximately 210.degree. F. at the kiln outlet to provide a fine particle slurry. A caustic liquid is also injected at the kiln inlet to facilitate extraction of the contaminants from the slurry. Separation of oil particles from the fine particle slurry is accomplished by first washing the slurry in a clarifier, followed by a second washing in flotation cell units, and finally subjecting the slurry to an aeration clarifier. A fatty acid or alcohol reagent is added at the aeration stage which produces a foam to which the oil particles adhere.
Paterson (U.S. Pat. No. 4,574,013) discloses a method for decontaminating soil containing halogenated contaminants by reaction schemes that are carried out in a slurry of soil and a nonaqueous reagent mixture. Peterson's nonaqueous reagent mixture contains an alkaline component and a sulfoxide catalyst. There are four possibilities suggested for the alkaline component: an alkali metal hydroxide, an alkali metal hydroxide/alcohol mixture, an alkali metal hydroxide/glycol mixture, or an alkoxide. The Peterson process employs a nonaqueous reagent mixture, and therefore when wet soil is to be decontaminated, a vacuum is first applied to remove any water prior to contacting the soil with the nonaqueous reagent mixture.
Weitzman (U.S. Pat. No. 4,662,948) discloses a method for removing polychlorinated biphenyls (PCB) and chlorinated dioxins from solids (particularly soil). In the Weitzman method, the contaminants are removed by contacting the solids with a nonaqueous liquid containing a halogenated hydrocarbon. Preferably, a smaller amount or polar organic solvent (normally methanol) is also used. The polar organic solvent apparently improves the wettability of the contaminated solids thus allowing the halogenated hydrocarbon to more easily extract PCB and dioxins.
In a study published by the U.D. Department of Commerce (National Technical Information Service #PB84-123637), funded by the United States Environmental Protection Agency and conducted by Rexnord, Inc., the requirements necessary for mobile systems for extracting spilled hazardous materials from excavated soils were analyzed. One result of the study was a listing of the characteristics necessary for an effective extraction fluid. Chief among these characteristics was a solvent possessing low volatility under ambient conditions.
Aqueous ammonia, a volatile solvent under ambient conditions would not be considered a suitable extraction fluid according to the above study and therefore, has not been used to decontaminate soil. However, aqueous ammonia has been used as a solvent for cleaning mechanical devices. For example, Cheek (U.S. Pat. No. 4,507,155) discloses a cleaning composition that includes a chlorinated hydrocarbon liquid, a petroleum distillate, an aliphatic alcohol, and aqueous ammonia. The composition consists of two phases, which must be shaken before application. The ammonia concentration of the composition is kept low (20-33% maximum) to prevent burns to the handler. The composition is disclosed as being suited fior removing dried printing ink from printing equipment such as printing rollers. The compositions also is reportedly useful as a spot remover for removing various stains from textile articles.
A need exists for relatively inexpensive methods for decontaminating large volumes of contaminated soil, found for example around hazardous waste dump sites, that would remove virtually all types of hazardouswastes, both organic and inorganic. Furthermore, as the volume f these hazardous wastes at dump sites accumulates, and as our understanding of the long-term health effects of these wastes increases, the need for such methods will undoubtedly increase.
Unfortunately, there are very few methods currently available that are suitable to decontaminate large quantities if contaminated soil. The few methods that are available are quite costly and are applicable to only a narrow spectrum of contaminants. Further, these methods either leave as their end-product small amounts of contaminants dissolved in large volumes of extracting solution or leave transformed chemicals in the soil which can continue to threaten our environment, even thiugh not currently recognized. These methods provide little help in dealing with the disposal of the large amounts of wastes found at hazardous waste dump sites.
The present invention provides an easy-to-use method for decontaminating large volumes of soil containing hazardous organic waste utilizing readily available equipment, and widely available and inexpensive materials. It is applicable to a broad spectrum of contaminants and, unlike prior art methods, leaves a relatively small volume of waste residue.